Hydrothermal activity associated with off-axis volcanism in the Peru Basin

Products of low temperature hydrothermal activity are widespread in the Per u Basin and are associated with late Tertiary oceanic island type intraplat e volcanics. Hydrothermal activity is still taking place as indicated by a series of sharp, high and narrow temperature anomalies over one of the volc anic cones. Submarine hydrothermal activity associated with off-axis volcan ism has been frequently observed elsewhere, but was usually found to be Lim ited to seamounts. In the Peru Basin a hydrothermal halo was found in sedim ents surrounding hydrothermally active seamounts in addition to hydrotherma l precipitates on the tops of the seamounts. Todorokite, birnessite, Fe-non tronite, goethite, and silica were found on top of young volcanic edifices and occur as coatings on volcanic rocks and in nuclei of manganese nodules. The hydrothermal precipitates in the sediments are Mg-Fe silicates, as is the case in the adjacent Bauer Basin. The proportion of hydrothermal precip itates in the sediments increases with depth in the cores, down to the appe arance of the basalt that indicates the beginning of intraplate volcanism 5 million years ago. Sediments overlying Late Tertiary volcanic rocks are lo cally enriched in hydrothermal material by solutions percolating upwards di rectly into the sediment. In these sediments, apatite and phillipsite appea r to have been precipitated directly from these ascending hydrothermal solu tions. (C) 1999 Elsevier Science B.V. All rights reserved.